DESCRIPTION (Applicant?s Abstract): Hermstein?s mathematical formulation of the matching law (1970) has been applied to data from operant conditioning procedures to disentangle the changes in responding attributable to drug-induced alterations in motivation from the changes attributable to drug-induced motor function impairment. The goal has been to develop an assay procedure and a classification system for the mode of behavioral action of drugs that have predictive value about the range of behavioral effects of drugs and their abuse potential. The behavioral procedure most often used in the studies is a Multiple Variable-Interval schedule (MultVI) consisting of five components that vary from 5 to 300 s. The generated response rate data are fitted by the single alternative equation of the matching law to obtain the value of the two parameters of the equation: k and rb. A common interpretation of k has been that it reflects, exclusively, the organism?s motor capacity to respond. The parameter rb is presumed to denote motivational factors. Results of studies conducted in our lab cast doubt on the above interpretation of the parameters. The same studies, however, confirm that k and rb are not affected by drugs in the same way, and that they may reveal different underlying actions of the drug. An alternative mathematical model, not burdened by theoretical implications of the matching law, is herein proposed. The model contains an additional parameter that reflects a third factor that underlies responding under operant procedures: stimulus control. Experiments will be conducted to test the validity of the proposed model by manipulating variables that affect (1) facility to respond, (2) reinforcer efficacy and (3) stimulus control. The effects of acute injections of d-amphetamine, gammahydroxybutyrate, morphine, diazepam and pimozide on the parameters of the model will be studied with rats trained to respond under a six-component MultVI schedule. The effects of chronic administration of the drugs and the development of tolerance or sensitization as denoted by the three parameters will also be investigated. The project will provide minority undergraduates with research experience by involving them in all phases of the study as Research Assistants.